The present invention relates to an automatic shift control system for automatically controlling the gear ratio of an automatic transmission of a vehicle, such as, an automobile.
Conventional systems of this type have been so designed that the running speed and the throttle opening of a vehicle are detected and the desired gear ratio region is determined in accordance with a shift pattern predetermined in accordance with these parameters thereby performing the desired multiratio gear shifts in response to such determinations. When a vehicle equipped with this automatic shift control system is run on a curved road, the vehicle is decelerated by releasing the accelerator pedal just before the curved road and in this condition the vehicle goes around the curve. Then, when the acceleration pedal is again depressed for acceleration near the end of the curve, downshifts of the transmission are effected in response to changes in the opening of the throttle valve linked to the pedal. However, this downshifting is delayed in time as compared with optimal operation of a manual transmission with which such downshifts are best performed manually at the beginning or in the middle of the curve. The delayed downshifting with an automatic transmission delays acceleration near the end of the curved road thus failing to ensure a smooth acceleration. The delayed downshifting also decreases the effectiveness of engine braking due to the downshifting on a descending curved road in addition to the abovementioned deficiencies.